Field
The present disclosure relates to techniques for communicating optical signals. More specifically, the present disclosure relates to a transceiver that cycles through groups of lasers having open ports and/or uses reduced transmit power to ensure safe operation.
Related Art
Parallel optical interconnects are widely used in board-to-board, rack-to-rack and box-to-box interconnect applications. In these applications, optical transceivers have aggregate capacity from 40 Gigabits per second to over 300 Gigabits per second. Typically, each optical transceiver provides 1, 4, or 12 separate transmitter channels, and each channel includes a vertical-cavity surface-emitting laser (VCSEL), as well as associated transmitter control and drive electronics. Moreover, each channel of information is usually conveyed on a separate optical fiber. However, products that include up to 24 optical lasers and optical detectors per transceiver are being considered. As data rates per channel have increased, there has been a corresponding increase in the transmit power per channel. In particular, the transmit power is typically dictated by the required optical power at the receiver and the associated loss of the optical link.
While such optical interconnect components are useful for transferring information and can be critical to the performance of the system, these optical interconnects also raise laser-safety concerns, specifically, the eye hazards associated with the use of such laser arrays. The primary laser-radiation hazard associated with VCSELs is caused by thermal effects that can cause injury to the eye. The low divergence angle of such laser light, particularly when used with focusing/collimating lens-based optical couplers (such as those included in low-cost, parallel optical-fiber connector assemblies) may pose a threat because the laser light can cause permanent damage within a fraction of a second (i.e., faster than the blink of an eye). VCSEL radiation, which is in the near-infrared (780-870 nm) range, can be invisible to many people. This increases the risk because this invisibility reduces the efficacy of the natural eye response (the human body's protective blink reflex is only responsive to visible radiation).
Furthermore, the use of VCSEL arrays spaced at a fraction of a millimeter (typically 250 μm) with optical couplers that include collimating optics results in multiple parallel beams that can be simultaneously coupled into the eye. Although the radiation at the near-infrared wavelengths is not visible, it can still be focused by the eye onto the retina with a localized intensity increase of up to 5 orders of magnitude. Therefore, even relatively small levels of laser power per VCSEL in the near-infrared can simultaneously couple into the eye, and can cause high-intensity heating of the human retina, potentially resulting in permanent damage.
Hence, what is needed is a transceiver without the above-described problems.